1. Field of the Invention
The invention relates to an autostereoscopic projection arrangement comprising at least one projector, a projection screen having a multitude of image rendering elements arranged in columns and rows, and at least one filter array having a multitude of filter elements arranged in columns and rows, in which the projector or the projectors project bits of partial information from views of a scene or object through one or several filter arrays onto the projection screen so as to make these bits of partial information visible on the image rendering elements.
2. Description of Prior Art
An arrangement of this type is described, e.g., in DE 206 474. This patent specification discloses a projection screen having a grid of lines each in front of and behind a ground glass screen (in viewing direction). The grids contain narrow, vertical lines which are alternatingly opaque and transparent, and through which is a stereopair of images is back-projected. The observer or observers looking through the grid in front see a spatial image, as either of the viewer's eyes is offered a different perspective. The drawback of this arrangement is that slight alignment errors of the line grids or the ground glass screen may cause irritating effects such as Moiré patterns.
U.S. Pat. No. 5,146,246 describes a two-view projection. In this arrangement, either of the observer's eyes is essentially offered only one view, i.e. either the right or the left one. Here again, a grid of lines each, i.e. a barrier screen, is arranged in front of and behind the projection screen (in viewing direction). This barrier screen is comprehensively disclosed as a pattern of opaque and transparent vertical stripes. A similar arrangement devised by the same inventor is described in U.S. Pat. No. 5,225,861. This is a back projection system, which projects a left-hand and a right-hand image each through a grid of opaque and transparent elements, in which, because of another grid of opaque and transparent elements, the observer's eyes are presented essentially disjoint views. This patent specification also describes vertical opaque and transparent stripes as grid elements.
For the two patent specifications mentioned last it is true again that the arrangements described require a large scope of alignment work. Moreover, the means of image separation described in addition are essentially suitable only for systems showing two views, so that the observer(s) of the stereoscopic image is/are hardly given any freedom of movement.
Patent application JP 9179090 describes a back projection system with a lenticular, in which at least two views of a scene are presented in a time-multiplex mode. Allocation of the back-projected views to the stripe segments on the projection screen, which correspond to the imaging directions of the lenticulars, is effected through controllable liquid crystal segments. These segments are switched to be either transparent or scattering, so that, depending on their respective states, a particular view is imaged by means of the lenticulars in always one or several defined directions. As a first disadvantage, this arrangement involves a large equipment outlay. In particular, it requires comprehensive control electronics. Moreover, despite the views presented in a time-multiplex mode at full resolution, the observer only sees one image per eye at a time, and at a reduced horizontal resolution. For flicker-free rendition, the arrangement further requires fast projection image display devices. The frame repetition rate of these image display devices must be the higher, the more views are to be presented, which adds to the cost of the arrangements.
U.S. Pat. No. 4,101,210 and U.S. Pat. No. 4,132,468 describe a stereo-projection for several views of a scene, in which, due to the imaging means provided on a screen (e.g., an emulsion), continuous, non-overlapping mosaic images with line structures are formed of several views. These mosaic images have virtually no gaps, i.e. their view portions are imaged quite next to each other. The said imaging means comprise, in particular, the use of lens arrays in combination with lenticulars.
DE 35 29 819 C2 describes a projection of several views through a lenticular. In this arrangement, projection of the strips of views to below each individual cylindrical lens is effected by the respective neighboring cylindrical lenses. The advantage of this is that the projector housings need not be particularly narrow in order to achieve the correct combination of views on the projection screen. The disadvantage is that, especially with large screen diameters, lenticulars of large size are needed.
DE 196 08 305 A1 discloses a back projection system in which two views are projected onto one screen through vertical barrier stripes. The mosaic image resulting from the two views is then made visible to the observer by a barrier screen in such a way that the observer's eyes see different views, which produces a 3D impression. The arrangement is characterized by a sliding mechanism, which shifts the barrier screen on the observer's side in accordance with the observer's eye position. One disadvantage of this arrangement is that only two views of a scene are used; another, that the control loop for ascertaining the eye position and accordingly shifting the barrier screen on the observer's side has a certain hysteresis, so that the observer sometimes sees a pseudoscopic image. In common embodiments, the arrangement is only suitable for a single observer.
DE 37 00 525 A1 describes a projection device with a lenticular. The projection area in this arrangement is curved. Among other disadvantages, the arrangement requires much space where large-size screens are used.
WO 98/43441 A1 describes a dynamic multiple-view projection system with shutters. The main disadvantage her is the extensive work involved in manufacturing the arrangement.
U.S. Pat. No. 2,313,947 discloses a multiple-view projection with two barrier screens comprising vertical barrier stripes. U.S. Pat. No. 2,307,276 also describes a multiple-view projection with barrier screens using vertical barrier stripes, in which, characteristically, a certain stripe width between the view stripes produced on the screen remains dark. This largely prevents pseudoscopic and double-image positions.
U.S. Pat. No. 4,872,750 describes a back-projection system with a barrier screen on the rear side, in which color images are produced by an overlap between separate RGB projections. The preferred means used here for spatial re-embodiment are lenticulars. The comprehensive equipment involved is a disadvantage.
Patent application DE 195 06 648 critically reviews, in the context of prior art in 3D imaging, the sudden change in perspective that occurs when the observer moves and that is due to the discrete number of views presented. The authors describe an autostereoscopic arrangement that avoids these disadvantages, and in which several views are presented in observable zones so that overlapping ranges are produced between the observation zones and so that the illumination intensity of the various observation zones is reduced at the margins. The optical imaging devices described include, among others, aperture diaphragms which, in transition regions, produce overlapping observation zones of two views each. The principle on which this patent application is based call for a considerable technical outlay if 3D images of larger size are required.
In DE 100 03 326 C2, the present applicant describes autostereoscopic methods and corresponding arrangements, in which the spatial impression for several observers without personal optical aids is produced by means of a wavelength filter array. The filter array, which is located in front of or behind an image display device, consists of a multitude of wavelength filters arranged in rows and columns, which are transparent to light of specified wavelengths or wavelength ranges and thus define discrete wavelength-dependent light propagation directions for the light emitted by the image display device. On the image display device, with its image rendering elements arranged in rows and columns, an image composed of several views of a scene or object is presented so that, due to the filter array, the observer's two eyes will see predominantly different selections of views. The disadvantage is that large-image projectors cannot readily be implemented in this way.